1. Field of the Invention
The present invention relates to insulating spacers for use in a gas-insulated electrical apparatus, and particularly relates to corrugated insulating spacers suitable for preventing reduction in dielectric strength due to the presence of electrically conductive foreign matters.
2. Description of the Prior Art
FIGS. 1A-1D show examples of prior art. In order to support high-tension electric conductors 2 in metallic pipes 1 filled with an insulating gas, generally, insulating spacers 3 having various shapes are used. The examples of the insulating spacers 3 include, for example, such a rod-like insulating spacer 3 having metal fittings at its opposite ends so as to be fixed between a high-tension conductor 2 and a metallic pipe 1 as shown in FIG. 1A, such a rod-like insulating spacer 3 having a metal fitting at its one end to be fixed to an inner wall of a metallic pipe 1 while supporting a high-tension conductor 2 at its other end portion through which the high-tension conductor 2 is passed as shown in FIG. 1B, such a rod-like insulating spacer 3 having metal fittings at its opposite ends to be fixed to an inner wall of a metallic pipe 1 while supporting a high-tension conductor 2 at its center portion through which the high-tension conductor 2 is passed as shown in FIGS. 1C(a) and 1C(b) to thereby stably support the high-tension conductor 2 to the metallic pipe 1, such a circular-conical insulating spacer 3 as shown in FIG. 1D, and so on.
In a gas-insulated electrical apparatus having such arrangements as described above, if electrically conductive foreign matters mix into the metallic pipe 1 and adhere to the insulating spacer 3 supporting the high-tension conductor 2, the creeping dielectric strength of the insulating spacer 3 is lowered substantially, so that the insulating reliability of the gas-insulated electrical apparatus is deteriorated markedly.
To cope with such a situation where electrically conductive foreign matters adhere to the insulating spacer 3, such an insulating spacer having a plurality of fins formed on a surface portion of the insulating spacer between the high-tension conductor 2 and the metallic pipe 1 for suppressing the deterioration in creeping dielectric strength has been proposed, for example, in Japanese Utility Model Publication No. 60-22743, Japanese Utility Model Unexamined Publication Nos. 58-31722, 58-31723, and so on.
In such a conventional insulating spacer, however, there have been problems in that fins are formed on the surface thereof equidistantly or at regular intervals, so that the creeping dielectric strength extremely varies with the position of attachment of the conductive foreign materials, and further in that if the longitudinal axis of the insulating spacer is made longer as the voltage of the gas-insulated electrical apparatus is made higher and higher, the number of the fins increases and the cost of moldings etc. becomes high.